This type of center mechanism of a tire vulcanizing machine, as shown, for example, in FIG. 5, has hitherto been composed of a hub portion (lower ring portion) 100a, which a lower clamp ring for holding a lower part of a bladder (not shown) is screwed into and fixed to; a cylindrical spacer portion 100b connected to the hub portion 100a for raising and lowering the bladder and the lower clamp ring; and a guide tube 103 fixed to an inner peripheral part of a lower heating platen 102 on a base 101, the hub portion 100a and the spacer portion 100b being fitted in the guide tube 103 so as to be ascendable and descendable.
Heating and pressurizing media passages 104 are formed within the hub portion 100a, and a heating and pressurizing media supply pipe 105a and a heating and pressurizing media discharge pipe 105b are connected to the heating and pressurizing media passages 104 by screwing-in or the like. A circulation head 106 is bolted onto the upper surface of the hub portion 100a, and a nozzle hole (not shown) of the circulation head 106 is in communication with one of the above-mentioned heating and pressurizing media passage 104.
A bottom wall part of the spacer portion 100b is bolted to a flange 107, and a center post cylinder 108 is upwardly passed through and supported by the flange 107. A piston rod 108a of the center post cylinder 108 penetrates the above-mentioned hub portion 100a and circulation head 106 to be slidable in a vertical direction, and has a leading end to which an upper clamp ring for holding an upper part of the bladder (not shown) can be secured.
A piston rod leading end of a bead lift cylinder 109, which has been supported upwardly by a bracket (not shown) on the base 101, is fixed to the flange 107. By the extending and contracting action of the bead lift cylinder 109, the above-mentioned hub portion 100a and spacer portion 100b are allowed to ascend and descend together with the center post cylinder 108.
Before vulcanization of a tire, therefore, the descending action of the hub portion 100a and the spacer portion 100b by the retracting action of the bead lift cylinder 109 together with the center post cylinder 108 positions the hub portion 100a and the spacer portion 100b onto the lower mold, while the leading end of the piston rod 108a protruding above the hub portion 100a is retracted by the center post cylinder 108, whereby the bladder grasped by lower clamp ring and upper clamp ring is inserted along the inside surface of unvulcanized tire set on a lower mold (not shown).
In this state, a heating and pressurizing media are fed into the bladder from a heating and pressurizing media supply and discharge device (not shown) via the following route, heating and pressurizing media supply pipe 105a→heating and pressurizing media passage 104→nozzle hole of circulation head 106, whereby the tire is vulcanized at a high temperature close to 200° C.